A process of hardening the face of steel, as armor plates, invented by Hayward A. Harvey of New Jersey, consisting in the additional carburizing of the face of a piece of low carbon steel by subjecting it to the action of carbon under long-continued pressure at a very high heat, and then to a violent chilling, as by a spray of cold water. This process gives an armor plate a thick surface of extreme hardness supported by material gradually decreasing in hardness to the unaltered soft steel at the back.